1. Field of the Invention
The present invention relates to a pre-warning method and a vehicle radar system, and more particularly, to a pre-warning method and a vehicle radar system capable of detecting target information in different dimensions.
2. Description of the Prior Art
As traffic safety is more important, vehicle safety equipment is getting more various. In addition to active or passive safety systems (such as anti-lock braking system, electronic brake-force distribution system, traction control system, electronic stability system, supplementary restraint system, etc.), pre-warning protection systems attract more attention. The pre-warning protection system uses an image self-recognition method of machine vision to detect possible situation which may cause danger, and sends out a warning light signal or an alarm sound to a driver in advance. The driver may change a driving direction according to the alarm signals, to avoid a traffic accident due to the driver's careless or blind side of vision.
Common pre-warning protection systems, such as an automatic cruise control, a blind spot detection system, an automatic braking system, a forward/rear collision warning system, a lane departure warning system, utilize frequency-modulated continuous waveform (FMCW) radar system in microwave form to perform target detections. These detections are performed by radar systems to transmit millimeter wave signals, receive reflected signals from targets, and compute information such as moving speeds, angles, ranges of the targets in relation to the radar system. In addition, to fit driving requirements, detecting ranges of the vehicle radar systems usually extend toward horizontal direction. In other words, the vehicle radar systems have detecting capability only in horizontal (Azimuth) dimension, so as to detect targets in driving direction.
Since the vehicle radar systems in the prior art have detecting capability only in horizontal dimension, if there are targets with high or low elevation angles, such as traffic signs, road signs, notice boards, pedestrian bridges, billboards, manhole covers, road humps, etc., the vehicle radar systems may make a false alarm, which may cause disturbance of drivers and unpredictable dangers. For example, please refer to FIG. 1, which is a schematic diagram of a forward collision warning system according to the prior art. As shown in FIG. 1, vehicles A, B drive in a road way S. According to a driving direction, the vehicle A is in front of the vehicle B. A front collision warning system is installed on a front of vehicle B, which detects traffic condition in the front and forms a radar range RG. Therefore, when the vehicle B is driving, the front collision warning system of the vehicle B keeps detecting target conditions within the radar range RG. Once a chance of collision is detected, the front collision warning system would alert or activate an automatic break mechanism. However, since the vehicle radar systems in the prior art have detecting capability only in horizontal dimension, target information in the vertical dimension would not be distinguished. Therefore, take FIG. 1 for example, when the front collision warning system of the vehicle B detects a road sign C, the front collision warning system may determine that the road sign C is on the driving road way, and send out an alert. Furthermore, the front collision warning system may activate an automatic break, which may cause dangers of colliding by the rear vehicles.
As can be seen, since the vehicle radar systems of the prior art detect target information only in horizontal dimension, miss detections and false alarms might happen because of external traffic and environment. Therefore, how to enhance a pre-warning accuracy of the vehicle pre-warning systems is a significant objective in the field.